Scientists in Japan claim to have developed a solution to a problem that has long plagued the creation of second generation biofuels from non-food biomass like weeds, waste, and paper.
The solvents needed for the creation of second generation biofuels tend to be highly toxic to microorganisms, necessitating complex process such as washing with water, separation by centrifugation and compression to remove these toxic solvents. The result of these detoxification processes is that the energy recovered from produced ethanol is less than that required to produce it.
This ‘negative energy balance’, in which increased ethanol production places more load on the environment, has long been considered a fundamental obstacle to the creation of second generation ethanol. A harsh solvent was needed to break down plant materials like cellulose, but this harsh solvent would kill the fragile microorganisms essential to the fermentation process needed to produce ethanol.
Researchers at Kanazawa University, Japan, have solved this problem by developing an innovative solvent for dissolving cellulose. The EC50, the concentration of a substance that reduces the growth of Escherichia coli to 50%, was found to be 158 g/L for the newly developed carboxylate-type liquid zwitterion, whereas the EC50 of an ionic liquid, one of the conventional solvents of cellulose, was 9 g/L. This indicates that the novel carboxylate-type liquid zwitterion shows 17 fold lower toxicity than the ionic liquid, claims a statement from the university.
Ionic liquids are salts that are liquid below 100ºC. They consist of various pairs of positively charged and negatively charged ions, and specific ionic liquids are known to be able to dissolve biomass and cellulose efficiently.
The scientists also examined the fermentation ability of the carboxylate-type liquid zwitterion on Estherichia coli, finding that 0.5mol/L of the substance resulted in a final ethanol concentration of 21g/L. The same experiment with the ionic liquid produced only 1g/L ethanol.
In another experiment, bagasse was used as a starting plant biomass for ethanol production without washing/separation processes. Fermentation in the presence of the carboxylate-type liquid zwitterion produced 1.4 g/L ethanol, while no ethanol was obtained with the ionic liquid due to its high toxicity (Figure 2), according to the scientists.
The researchers’ findings suggest that converting plant biomass with the carboxylate-type liquid zwitterion, plant biomass could be converted into ethanol in a single reaction without the need for washing or separation processes.
As the press release from Kanazawa University notes: “This should be a big step forward in the production/utilisation of second generation biofuel ethanol through reducing large amounts of energy input.”
The findings have been published in the Journal of American Chemical Society.